This application claims the priority benefit of Japanese application serial no. 2001-035920, filed Feb. 13, 2001.
1. Field of the Invention
The invention relates to an optical disc recording apparatus and medium. More particularly, the invention relates to an optical disc recording apparatus and medium for an erasable optical disc.
2. Description of Related Art
The recordable optical disc, in general, comprises a write-once type disc, such as CD-R (Compact Disc-Recordable), and an erasable disc, such as CD-RW (Compact Disc-ReWritable). As shown in FIG. 5, the laser power used for the overwrite record for the erasable optical disc is varied among three values, a recording power Pw an erasing power Pe and a cooling power Pc. The recording power Pw is the power to raise the temperature of a recording layer (phase-change layer) of the erasable optical disc up to its melting point, the cooling power Pc is a low power for quenching the recording layer from the melting point to a temperature where the recording layer becomes an amorphous state, and the erasing power Pe is the power to raise the temperature of the recording layer above a glass transition point.
During the recording process of the optical disc, an optimum recording power Pwo and an optimum erasing power Peo respectively vary according to different disc types, recording apparatuses and recording speeds. Therefore, when the recording is actually performed, an operation of recording power calibration, also known as optimum power control (OPC), is performed before recording information, in order to set the optimum recording power Pwo and the optimum erasing power Peo that match the disc type, the recording apparatus and the recording speed.
The conventional OPC operation of an erasable optical recording apparatus is described below. As shown in FIG. 6, a data area for storing data, and a test recording area (power calibration area, PCA) for setting an optimum recording power of the laser beam, are arranged on a recording surface of the optical disc. The PCA area is located at the most inner circumference of the optical disc, and composed of a test area and a count area, wherein the test area comprises 100 partitions and each of the partitions includes 15 frames. One OPC operation uses one partition and records a test signal by a 15-step laser power corresponding to the 15 frames. The test signal is an eight-to-fourteen modulation (EFM) signal composed of a pulse train with a time interval that is 3xcx9c11 times a base time interval T. The base time interval T is a standard speed (1xc3x97), and a period of frequency 4.32 MHz and of about 230 nsec. In addition, 9 pits with different lengths are recorded in the frame.
By illuminating the frame with the laser beam and detecting the reflecting beam from the optical disc, the test signal is reproduced and the modulation m, used as an indication for showing the amplitude of the respective reproducing RF signal, is determined. The determination of the modulation m utilizes the reproducing RF signal before AC coupling.
m=I11/Itopxe2x80x83xe2x80x83(1)
As shown in FIG. 7, I11 represents a reproducing RF (radio frequency) signal from the pit and land (portions between the pit and the land) of 11T, I3 represents a reproducing RF signal from the pit and land of 3T, and Itop represents a mirror reflecting lever of the land portion. The modulation degree m varies corresponding to the recording power Pw. When the recording power Pw is low, the modulation degree m is smaller due to the small amplitude of the reproducing RF signal. As the recording power Pw becomes larger, the modulation degree m becomes large because the amplitude of the reproducing RF signal also becomes large.
When the optimum recording power Pwo is determined by the modulation degree m, the following parameter xcex3 calculated from the characteristic of the modulation degree m is used.
xcex3=(dm/dPw)xc3x97(Pw/m)xe2x80x83xe2x80x83(2)
Namely, the parameter xcex3 is the differential of the characteristic of the modulation degree. A target value xcex3target of the parameter xcex3 is recorded in advance in the optical disc, serving as an absolute time in pregroove (ATIP) information. As shown in FIG. 8, the characteristic of the parameter xcex3 is calculated by the equation (2) above from the characteristic of the modulation degree m, and the target value xcex3target is then used to calculate the target recording power Ptarget.
In addition, because a coefficient xcfx81, the ATIP information, used for calculating the optimum recording power Pwo from the target recording power Ptarget has been previously recorded, the optimum recording power Pwo can be calculated by using the coefficient xcfx81 according to the following equation (3).
Pwo=xcfx81xc3x97Ptargetxe2x80x83xe2x80x83(3)
The optimum recording power Pwo is set to the recording power and used for recording signals. Additionally, in the following equation (4), the optimum erasing power Peo is set from the optimum recording power Pwo by using a constant coefficient xcex5 (a ratio of the erasing power over the recording power) of the ATIP information recorded in the optical disc. The cooling power Pc is a constant power.
Peo=xcex5xc3x97Pwoxe2x80x83xe2x80x83(4)
In the conventional recording and erasing methods described above, the method, where the optimum recording power Pwo is determined by the OPC operation, the optimum erasing power Peo is calculated by multiplying the optimum recording power Pwo with the coefficient xcex5 and the cooling power is a constant, uses few parameters and is easily set. However, under the combination of the optical disc and the optical pick up, recording power is affected by dispersion. Therefore, when the recording power increases, the erasing power becomes large and thus the total of the recording and erasing powers also increases. As a result, the durability, that the optical disc can be repeatedly recorded, degrades. In contrast, due to the dispersion influence on the recording power, when the recording power decreases, the erasing power also becomes small, causing a problem where the erasing property gets worse. The durability, that the optical disc can be repeatedly recorded, represents how many times the data can be recorded at the same location on the optical disc, and regarding the data being reproduced after being recorded, the durability means the recording times that both the jitter and the modulation degree m satisfy the preset specification.
Therefore, it is an object to overcome the foregoing issues by providing an optical recording apparatus and an optical recording medium. Under the combination of the optical disc and the optical pick up, even if the dispersion of the recording power becomes large, the degradation of the durability, that the optical disc can be repeatedly recorded, can be suppressed. In addition, even if the dispersion of the recording power becomes small, the erasing power is not smaller than a certain range, which prevents the erasing property from getting worse.
According to the above and other objectives, the present invention provides an optical recording apparatus used for recording an erasable optical disc, comprising a means for calculating an optimum recording power, capable of varying a recording power to perform a recording process on a test recording area of the erasable optical disc, and then calculating an optimum recording power according to signals obtained by reproducing the test recording area; and a means for calculating an optimum erasing power from the optimum recording power and a coefficient corresponding to the optimum recording power. Thereby, the optimum recording power and the optimum erasing power are used for recording the erasable optical disc. In addition, the coefficient becomes smaller when the optimum recording power becomes larger. The coefficient corresponds to the optimum recording power for setting up the optimum erasing power within a certain range.
Therefore, under the combination of the optical disc and the optical pick up, even though the dispersion of the recording power becomes large, the erasing power is not greater than a certain range; therefore, the total of the recording power and the erasing power can be restrained and the degradation of the durability, that the optical disc can be repeatedly recorded, can be suppressed. In contrast, even if the dispersion of the recording power becomes small, the erasing power is not smaller than a certain range, which prevents the erasing property from getting worse.
The invention further provides an erasable optical recording medium, having a coefficient for calculating an optimum erasing power from an optimum recording power, wherein the coefficient corresponds to the optimum recording power and is recorded on the erasable optical recording medium. The foregoing coefficient becomes smaller when the optimum recording power becomes larger. The coefficient corresponds to the optimum recording power for setting up the optimum erasing power within a certain range.
Therefore, as the optical recording medium is loaded into the optical recording apparatus, under the combination of the optical disc and the optical pick up, even though the dispersion of the recording power becomes large, the erasing power is not greater than a certain range; therefore, the total of the recording power and the erasing power can be restrained and the degradation of the durability, that the optical disc can be repeatedly recorded, can be suppressed. In contrast, even if the dispersion of the recording power becomes small, the erasing power is not smaller than a certain range, which prevents the erasing property from getting worse.